Electric arc heating and acceleration of gases



ggrmwa 1957 R. c. ESCHENBACH ETAL 3,301,995

ELECTRIC ARC HEATING AND ACCELERATION OF GASES Original Filed March 9, 1962 /N|/EN7O/?S RICHARD C. ESCHENBACH GEORGE M. SKINNER RAYMOND J. SARLITTO ROBERT J. WICKHAM A T TOP/VEV United States Patent 3,301,995 ELECTRIC ARC HEATING AND ACCELERATION 0F GASES Richard C. Eschenbach, Indianapolis, Ind., George M.

Skinner, Murray Hill, N.J., Raymond J. Sarlitto, Indianapolis, Ind., and Robert J. Wickham, Caldwell Township, N.J., assignors to Union Carbide Corporation, a corporation of New York Continuation of application Ser. No. 178,665, Mar. 9, 1962. This application Dec. 2, 1963, Ser. No. 328,783 Claims. (Cl. 219-121) This application is a continuation of our copending application Serial No. 178,665, filed March 9, 1962, now abandoned.

This invention relates to an improved apparatus for heating atmospheric air or other gases to extremely high temperatures and discharging same at extremely high velocities. More particularly, it relates to the heating of such gases within a confined space by means of a high voltage electric arc.

Present day industrial technology has developed to the extent that research and test procedures often must be conducted under simulated conditions in the laboratory before tests under actual conditions can be made. Simulating such conditions on a laboratory basis can be in many cases extremely difficult. The aviation industry, for example, encompassing the field of space exploration, missile development, propulsion equipment, etc. must produce gas velocities of many times the speed of sound and/ or temperatures far exceeding the melting points of most common construction materials for such laboratory testing. Devices capable of producing such gas velocities and temperatures on a laboratory basis are largely unobtainable. The advantages to be gained from such testing devices are obvious in terms of making it possible to pretest airframe shapes, material durability at elevated temperatures and the like. Such pretesting is, of course, necessary to the protection of human life and the successful operation and recovery of extremely expensive unmanned vehicles.

Electric arcs appear to be the most practical heat source for supplying the energy required to achieve the high velocities and temperatures required for such testing. In such applications it is of prime importance to get a maximum amount of the power supplied to the arc device to be transferred to the hot gas efliuent. It has been found that if higher power to the arc device is achieved solely through current increases, such additional power is used up primarily in heating the electrodes and their cooling fluid streams. Voltage increases, on the other hand, are substantially transmitted as higher heat to the arc gas.

In the case of various test devices, such as aerodynamic wind tunnels and materials testing equipment, extremely high gas velocities are required. These high exit velocities are achieved by expanding high temperature, high pressure gas.

In a device extremely useful for achieving higher are voltages, air or other gases under pressure is introduced into a chamber through a plurality of apertures. An arc is then established through the chamber between a cup electrode and a nozzle electrode, the flow of gas directing the are along the nozzle electrode. A magnetic field induced by a field coil surrounding at least one of the electrodes further directs the arc and at the same time increases the arc voltage. Air having an extremely high heat content is then discharged at high velocity from the end of the electrode nozzle. This device is useful for power levels of about 500,000 watts. In contrast, the device of the present invention is capable of operating at power levels as high as about 4 million watts at pressures up to as high as 1500 p.s.i.a.

Patented Jan. 31, 1967 It is accordingly the primary object of this invention to produce an electric arc apparatus which is capable of operating at extremely high voltages and pressures so as to heat gases to unusually high temperatures and to accelerate the same to exceptionally high velocities.

It is another object to provide an electric arc apparatus which has improved means of injecting gas to be heated into such apparatus.

It is a further object to provide electrode configurations which are capable of handling high levels of current and voltage with substantially no electrode loss.

Other objects and advantages will be apparent from the accompanying description and drawing in which the sole figure is a cross-section showing the construction details of a preferred embodiment of the invention.

The objects of the invention are accomplished generally by an electric arc apparatus which has a first watercooled tubular electrode closed at one end and which has a length to inside diameter (L/D) ratio in the range of between about 5 and about 30. A second tubular watercooled electrode open at both ends is axially spaced from the open end of the first electrode. This second tubular electrode is preferably the cathode and has a L/D ratio of between about 5 and about 40. Further, the ratio of the inside diameter (I.D.) of the the first electrode to the ID. of the second electrode is between about 2.5 and about 0.5. In addition to this, the ratio of current to the ID. of the second electrode is broadly between about 50 and 2000 amps/inch. A nozzle outlet is carried by the second electrode at one end thereof. A water-cooled chamber surrounds and is substantially greater in diameter than the space between the two electrodes. A plurality of gas injection means are rotatably mounted in the walls of the water-cooled chamber. Such injection means includes a tubular member provided with an orifice which directs the gas to be heated into the chamber. Clamping means maintains the first electrode, second electrode, and the chamber as an integral unit regardless of pressure achieved in the chamber. The apparatus is also provided with means for supplying electric power to the two electrodes. The first and second electrodes are preferably constructed of copper because of its high electrical and thermal conductivity. Such material is useful to minimize electrode damage in the presence of oxidizing atmosphere. When certain gases other than air are to be heated, for example argon, helium, hydrogen, and nitrogen; tungsten or tungsten containing emissive material such as thoria is the preferred cathode material. Silver, aluminum, steel and molybdenum are the other useful electrode materials.

The instant high voltage are device is able to supply air or other gases at extremely high temperatures and velocities and at suitable power efficiencies to the air or other gas. Atmospheric air or other gases are introduced into the chamber through the plurality of injection means. An arc is then established through the chamber between the first electrode and the second electrode, the flow of the gas directing the are along the second electrode. In the preferred form of the invention a magnetic field surround the electrodes induced by a field coil further directs the arc and at the same time increases the arc voltage. Air having an extremely high heat content is then discharged at high velocity from the end of the electrode nozzle.

Referring now the drawing, a preferred embodiment of the present invention comprises a hollow cup shaped electrode 10 open at one end and provided with a closing member 12 at the other. The electrode 10 is supported within a water-cooled holder 14 spaced from said electrode 10 and forming an annular chamber therebetween. A sleeve 20 extends within the chamber and divides the chamber into annular chambers 16 and 18. Member 22 and O-ring seal 24 forms a closure between the forward end of sleeve 20 and holder 14. The member 22 is protected from damage from heat during arc initiation by copper ring 32. Nut 26 in conjunction with member 12 provides a closure between the other end of sleeve 20 and holder 14 and also provides a coolant inlet passage 28 and outlet passage 30. Are power is supplied to the electrode through nut 26.

In operation, the electrode 10 is cooled by passing cooling water in through inlet passage 28, then through annulus 18 formed by the sleeve and electrode 10. The water then passes out through annulus 16 formed by holder 14 and sleeve 20 to outlet 30.

Chamber 34 surrounds and extends beyond the open end of cup shaped electrode 10. The chamber 34 consists of a hollow cylindrical member 36 the rear end of which is closed by nut 38 and the forward end of which is closed by flange 40 and ring 42. Ring 42 is chamfered for forming a smooth entrance to the front electrode 44. Flange 40 provides a coolant inlet passage 46 and annuli 48 and 50 which are connected by a plurality of passages 52. The member 36 is provided with a plurality of passages 54 each of which are formed by drilling a hole and then partially plugging the hole with rod 56 in order to make passage 54 relatively small in diameter for high velocity water cooling. Nut 38 and member 36 form an annular chamber 58 which communicates with outlet 60 in the member 36. The chamber 34 is cooled by passing cooling water from inlet 46 through annulus 50, through passages 52 and annulus 48 to passages 54 The water exits through annular chamber 58 and outlet 60.

A nut 64 is connected to flange 40 by a plurality of bolts 65. Threaded into the nut 64 is electrode holder 66. Positioned within and radially spaced from holder 66 to form an annular chamber therebetween is front tubular electrode 44. Electrode 44 is joined to chamfered ring 42 by a front joint 68. Electrode 44 has a nozzle outlet 62 threaded to the forward end thereof. Sleeve 70 positioned in the annular chamber between the holder 66 and electrode 44 divides the chamber into annular chambers 72 and 74.

Nozzle flange 76 is threaded to the forward end of holder 66 and provides a water outlet passage 78 from annular chamber 72. Nozzle flange 76 also supports the nozzle outlet 62 and provides a means for connecting the are power supply to the device.

In operation, the front electrode 44 is cooled by passing cooling water from inlet 46 and annulus 50 through annular chamber 72 and then out through passage 78.

Annulus 74 formed by sleeve 70 and the electrode holder I 66 provides a dead water shield around the sleeve 70. That is, the water does not flow through the annulus. This water aids in reducing the pressure on the sleeve when high pressure, high velocity water is used to cool the electrode. Sleeve 70 has been provided with spacers 80 to insure that the width of annulus 72 will remain more or less constant thereby insuring a more uniform flow of cooling water even when the are tends to localize for a short period of time at some spot along the inner face of the electrode. When the are so localizes, the electrode will become excessively heated at that spot thereby causing it to bend or otherwise warp around the periphery of the electrode so as to restrict the flow of water through the annulus. This merely aggravates the situation by making the hot spot hotter until the electrode finally burns through. By providing the spacers 80 along the length of the electrode and around its periphery, the warping or bending can be kept to a minimum so that the situation arising from the hot spots will not become aggravated. The number of spacers and their spacing would, of course, depend upon the length and diameter of the electrode. For an electrode having a length of 30" and an OD. of 2", sets of spacers spaced so as to divide the electrode into three equal lengths with each set having three spacers spaced apart have been 4 found to be suitable. It should be noted that the crest of the spacers should be kept as small or as pointed as structurally possible in order to insure that the flow will not be unduly restricted.

A plurality of gas injection means 13A, 13B, and 13C are rotatably mounted in the cylindrical hollow member 36. These gas injection means consist of two tubes 19 and 21 which are kept in concentric alignment with the opening 21A of the shell 36 through the nut 25 and fitting 23. Tube 21 is brazed to tube 19. Tube 21 contains an aperture 27 which through rotation of the tube 21 is able to impart either a vortex flow or an axial flow of the air or other gas being admitted to the device. That is, it can be directed so as to emit the air in the direction of the axis of the torch or it can be directed so as to emit the air tangentially to the shell 36 of the chamber 34, that is, normal to the axis of the torch. Tube 21 is rotated within fitting 23 by loosening nut 25. Thus either axial or vortex flow can be obtained. The velocity of the flows can also be easily varied by replacing the tubes and using different size apertures. Furthermore, the depth that the tube extends into the chamber can be easily varied so as to vary the strength or momentum of the flow. That is, in general, as the depth of the tube is increased, the strength or momentum of the flow is increased. This is especially useful when vortex flow is used since the increasing of its strength will increase the are voltage. If, however, the depth of the tube becomes excessive, the uniformity of the vortex flow as it nears the axis will be decreased. Consequently, this gas sheath should have a diameter of no less than 1 /2 times the diameter of the front electrode in order to insure that the vorticity will be properly maintained. The maximum depth of the tubes for inlets 13B and 13C, therefore, should be such that the locus of points formed by the tubes apertures is a circle having a diameter of not less than one and a half times the diameter of the front electrode.

Most of the gas to be heated is introduced to the torch through injection means 138 and 13C. Means 13A is used primarily to cool the electrode insulator 29 and heat shield 51.

Are initiating means 35 communicates with chamber 34- through the walls of the flange 40. Such means includes a carbon electrode 37 threaded into a rod 39 which is secured to an air cylinder 41. An appropriate power supply is connected to nut 26 and nozzle flange In operation, a small amount of air or other gas to be heated is admitted under pressure to chamber 34 through injection means 13A, B and C. Alternating current or direct current with straight or reverse polarity may be used as desired. However, for maximum arc voltage and overall torch efficiency, it is preferred that the front electrode act as the cathode when operating on direct current. The are is established by moving the carbon electrode 37 into close proximity with the open end of the rear electrode 10 until a spark is initiated. Carbon electrode 37 is then withdrawn so as to establish an are between rear electrode 10 and front electrode 44. The starting means may be automatically operated. For example, an air cylinder 41 could be used. The quantity of air is then increased as desired. The are that is finally established will extend from an area along the length of the rear electrode 10 to an area along the length of the front electrode 44.

The general configuration of the torch permits a portion of the air to flow into and out of the rear electrode and then through the front electrode so long as the air is introduced at a suffieient velocity through apertures 27. That is, in starting the torch if the inlet velocity is greater than 0.25 Mach, then there will be a suflicicnt pressure gradient within the chamber between its outer wall and the area near the torch axis to force a substantial portion of the air into the rear electrode. This results in a longer are which increases the are voltage.

Electrode erosion has been minimized by the addition of the water-cooled copper field coil 49 which tends to rotate the are around the electrode area. In addition to preventing electrode erosion, the coil will also tend to elongate the are so as to increase the arc voltage as well as spread out the arc area so as to permit greater overall currents with workable current densities.

Generally, it is highly desirable to introduce the air into the chamber 34 in a swirling or vortex fashion. Such flow enables a relatively high are voltage level to be maintained for a given current. This results in greater torch efiiciencies in that more of the power being supplied to the torch is getting to the gas. Even though greater efiiciencies may be achieved with a vortex flow, it is sometimes desirable that axial flow be used. For example, axial flow may be required for aerodynamic applications such as wind tunnel testing. It is highly desirable, therefore, that the inlets 13A, B and C to the chamber 34 be readily changeable. This has been accomplished by the previously described fitting used to join the injection means 13A, B and C to the chamber shell 36.

In a high power, high pressure torch such as this, there is a tremendous force being exerted on the electrodes and their supporting structure. Such force tends to pull the electrode away from the torch body, or more specifically it tends to pull the electrodes away from the chamber 34. For example, in the present device with a chamber pressure of 1500 p.s.i.a., there would be a force of about 20,000 lbs. exerted axially against the electrodes and their supporting structure. In this improved torch, this tremendous load is transmitted from the electrode and its water jacket 14, to the plurality of tie bolts through the stainless steel flange 47, insulator 33, stainless steel flange 37 and insulator 29. From the tie bolt 15, the load is then transmitted to the front chamber closure flange 40. Thus, the tie bolts, rather than the walls 36 of chamber 34 carry the axial load exerted by pressure within the chamber.

Suitable materials for the insulators have been found to be Synthane, Bakelite, Formica, and nylon. The insulator 29 is kept from melting during operation by the heat shield 51. Suitable matreials for the heat shield have been found to be fused silica, micarta, and transite. However, materials exhibiting like properties for both the insulators and the shield could also be used.

For a given inside diameter of electrode, the length of the rear electrode should be such that the arc will remain stable without having too great a tendency to run to the electrode bottom. Specifically, if the length is too short, the arc will run to the bottom causing severe e1ectrode erosion, whereas if the length becomes excessive the arc will become unstable. Therefore, the L/D ratio of the electrode should decrease slightly as the diameter increases. Generally, the L/ D should be from about 5-30. Optimumly for a inch inside diameter electrode the L/D should be from about 10-20, while for a 1 /2 inch diameter, the L/D should be from about 6-12.

The L/D of the front electrode should be such that there be a sufficient distance between the arc termination area and the entrance to the nozzle outlet to allow the gas flow to become uniform and yet not cause an undue loss of enthalpy in the gas. Specifically, if the length of the electrode is too short the arc will terminate too close to the entrance to the nozzle thus not allowing sufiicient time for the gas fiow to become uniform prior to entering the nozzle after leaving the arc area. On the other hand, if the length becomes excessive, much of the heat in the gas will be lost to the electrode. Generally, the L/D should be from about 5-40. However, since the length of the arc is greatly influenced by the cross-sectional area of the nozzle throat as compared with the crosssectional area of the electrode, the L/D should be optim-umly chosen on this basis. That is, the smaller the cross-sectional area of the throat as compared with the cross-sectional area of the electrode, the shorter will be the arc of a given current and gas flow rate. Optimumly, then, if the throat area is less than half of the electrode area the L/D of the electrode should be from about 5-30, While if the throat is greater than half the electrode area, the L/D should be from about 10-40. However, under the latter condition, if higher enthalpies are desired with lower flow rates and therefore less power, since power is a function of flow the L/D could, as in the first condition, be between 5-30.

As a further aid in maintaining arc stability and minimizing rear electrode erosion, the ratio of the I.D. of the rear electrode to the I.D. of the front should be kept between about 2.5 and 0.5. That is, if the ratio becomes too great the arc will become unstable, while if it becomes too small erosion will occur at the open end of the rear electrode.

In addition to the ratio of the I.D. of the rear electrode to the I.D. of the front, maximum operating efiiciencies can be achieved if the ratio of the current in the device to the I.D. of the front electrode is kept between about 50 and 2000 amps/inch. That is, if the ratio becomes too small, the arc will become unstable, whereas if the ratio becomes too large, electrode erosion will occur because of high current densities. Optimumly, for maximum operating efiiciencies at gas enthalpies of between about 2000-6000 B.t.u./lb., the ratio should be between about and 600.

The following examples illustrate the operation of the torch. In the examples, apparatus of the type depicted in the accompanying drawing was used. In both examples, the chamber had 6 inlets spaced in 3 rows with 2 inlets in each row spaced apart. Also, in both examples, a field coil having a magnetomotive force of 39 kiloampere turns was placed around the rear electrode, the direction of the field being toward the rear of the rear electrode.

Example 1 In this run, the rear electrode had 1.5 inch I.D. and a length of 16 inches, while the front electrode had an I.D. of 1.5 inches and a length of 20 inches. The nozzle electrode had a throat diameter of .505 inch. Air was supplied tangentially to yield a vortex flow at a rate of 6700 c.f.h. With the front electrode acting as the catliode, 400 amperes was supplied to the device. The are voltage was 2040 v. The chamber pressure was 137 p.s.i.a. The total power to the torch was 816 kw. of which 603 went to the gas yielding a torch efficiency of 74 percent. The calculated gas exit velocity after expansion to a pressure of one atmosphere was 8150 ft./sec. The gas chamber temperature and enthalpy was 5000 K. and 4100 B.t.u./lb. respectively. The are effluent was blue indicating very little electrode erosion.

Example 11 In this run the rear electrode had an I.D. of 1.5 inches and a length of 16 inches, while the front electrode had an I.D. of 1.5 inches and a length of 30 inches. The nozzle electrode had a throat diameter of .438 inch. Air was supplied tangentially at the rate of 21,000 c.f.h. With the front electrode acting as the cathode 405 amperes was supplied to the device. The arc voltage was 4430 v. The chamber pressure was 520 p.s.i.a. The total power to the torch was 1795 kw. of which 1055 kw. went to the gas yielding an efficiency of 59 percent. The calculated gas exit velocity after expansion to a pressure of one atmosphere was 8000 ft./sec. The gas chamber temperature and enthalpy was 3750 K. and 2300 B.t.u./ lb. respectively. Again the arc effiuent was blue indicating very little electrode erosion.

While the invention has been described with reference to the use of a particular piece of apparatus, it should be understood that other apparatus modifications could be used, all within the spirit and scope of this invention. For example, the sleeves were used particularly as a convenience for using standard pipe sizes for the electrodes and the electrode holders, the sleeves being the means to attain the proper cooling annulus width. The annulus width could just as well be formed by proper sizing of the electrode and the electrode holder. Likewise, the spacers could be formed as part of the sleeve or as part of the electrode or if no sleeve is used, as part of the electrode holder. Furthermore, the spacers could be formed through the use of solder or other means.

What is claimed is:

1. An electric arc gas heater comprising a first tubular water-cooled electrode having closure means at one end thereof and being open at the other end and having a length to diameter ratio of between about to about 30; a second tubular water-cooled electrode open at both ends and axially spaced from the open end of said first electrode and having a length to diameter ratio of between about 5 to about 40, the ratio of the inside diameter of said first tubular electrode to the inside diameter of said second tubular electrode being between about 2.5 to 0.5; and the ratio of current to inside diameter of said second electrode being between about 50 and about 2000 amp/inch; a nozzle outlet carried by said second tubular member at one end thereof; a watercooled chamber of substantially greater diameter than and surrounding the space between said two electrodes; a plurality of gas injection means mounted in the walls of said chamber and including a tubular member provided with an orifice for directing the gas to be heated into said chamber.

2. A gas heater as set forth in claim 1 and including arc initiating means.

3. A gas heater as set forth in claim 1 wherein an electric field coil circumferentially surrounds at least one of said electrodes.

4. An electric arc gas heater comprising a first tubular electrode having closure means at one end thereof and being open at the other end and having a length to diameter ratio of from about 5 to about 30; a second tubular electrode open at both ends and axially spaced from the open end of said first electrode and having a length to diameter ratio of from about 5 to about 30, the ratio of the inside diameter of said first tubular electrode to the inside diameter of said second tubular electrode being from about 2.5 to about 0.5 and the ratio of current to inside diameter of said second electrode being from about 50 to about 2000 amps/inch; a nozzle outlet having a throat section and an expansion passage of increasing diameter carried by said second tubular memher at one end thereof, the cross-sectional area of said throat section being less than /2 the cross-sectional area of said second tubular electrode; a Water-cooled chamber of substantially greater diameter than and surrounding the space between said two electrodes; a plurality of gas injection means mounted in the walls of said chamber and including a tubular member provided with an orifice for directing the gas to be heated into said chamber.

5. An electric arc gas heater comprising a first tubular electrode having closure means at one end thereof and being open at the other and having a length to diameter ratio of from about 5 to about 30; a second tubular electrode open at both ends and axially spaced from the open end of said first electrode and having a length to diameter ratio of from about to about 40, the ratio of the inside diameter of said first tubular electrode to the inside diameter of said second tubular electrode being from about 2.5 to about 0.5 and the ratio of current to inside diameter of said second electrode being from about 50 to about 2000 amps/ inch; a nozzle outlet having a throat section and an expansion passage of increasing diameter carried by said second tubular member at one end thereof, the cross-sectional area of said throat section being greater than /2 the cross-sectional area of said second tubular electrode; a water-cooled chamber of substantially greater diameter than and surrounding the space between said two electrodes; a plurality of gas injection means mounted in the walls of said chamber and including a tubular member provided with an orifice for directing the gas to be heated into said chamber.

6. An eleltric arc air heater comprising a first tubular water-cooled electrode having closure means at one end thereof and being open at the other and having an inside diameter of about /4" and a length to diameter ratio of between about 10 to about 20; a second tubular watercooled electrode open at both ends and axially spaced from the open end of said first electrode and having a length to diameter ratio of between about 5 to about 40, the ratio of the inside diameter of said tubular electrode to the inside diameter of said second tubular electrode being between about 2.5 to about 0.5; and the ratio of current to inside diameter of said second electrode is between about 50 to 2000 amps/inch; a nozzle outlet carried by said second tubular member at one end thereof; a water-cooled chamber of substantially greater diameter than and surrounding the space between said two electrodes; a plurality of gas injection means mounted in the walls of said chamber and including a tubular member provided with an orifice for directing the gas to be heated into said chamber.

7. An electric arc gas heater comprising a first tubular water-cooled electrode having closure means at one end thereof and being open at the other and having an inside diameter of about 1 /2" and a length to diameter ratio of between about 6 to about 12; a second tubular watercooled electrode open at both ends and axially spaced from the open end of said first electrode and having a length to diameter ratio of between about 5 to about 40; the ratio of the inside diameter of said first tubular electrode to the inside diameter of said second tubular electrode being between about 2.5 to about 0.5 and the ratio of current to inside diameter of said second electrode is between about 50 and about 2000 amps/inch; a nozzle outlet carried by said second tubular member at one end thereof; a water-cooled chamber of substantially greater diameter than and surrounding the space between said two electrodes; a plurality of gas injection means mounted in the walls of said chamber and including a tubular member provided with an orifice for directing the gas to be heated into said chamber.

8. An electric arc heater comprising a first tubular water-cooled electrode having closure means at one end thereof and being open at the other and having an L/D ratio of between about 5 to about 30; a second tubular water-cooled electrode open at both ends and axially spaced from the open end of said first electrode and having an L/D ratio of between about 5 and about 40, the ratio of ID. of said first and second tubular electrodes being from about 2.5 to about 0.5 and the ratio of current to ID. of said second electrode being about -600 amps/ inch; a nozzle outlet carried by said second tubular member at one end thereof; a water-cooled chamber of substantially greater diameter than and surrounding the space between said two electrodes; a plurality of gas injection means mounted in the walls of said chamber and including a tubular member extending into said chamber provided with an orifice for directing the gas to be heated into such chamber; the maximum extension of said tubular member into said chamber being such that the locus of points formed by said orifice is a circle having a diameter of at least 1 /2 times the inside diameter of said second tubular electrode.

9. An electric arc gas heater comprising a first tubular water-cooled electrode having closure means at one end thereof and being open at the other and having an L/D ratio of from about 5 to about 30; a second Water-cooled tubular electrode open at both ends and axially spaced from the open end of said first electrode and having an L/D ratio of between about 5 to about 40, the ratio of ID. of said first electrode to the ID. of said second e1ectrode being between about 2.5 and about 0.5, the ratio of current to ID. of said second electrode being between about 50 and 2000 amps/inch; a water jacket surrounding and radially spaced from said second tubular electrode so as to form an annular space therebetween; a plurality of spacers positioned in such annular space be tween said water jacket and said second tubular electrode for maintaining the said annular space therebetween; a water-cooled chamber of substantially greater diameter than and surrounding the space between said two electrodes; a plurality of gas injection means mounted in the walls of said chamber and including a tubular member provided with an orifice for directing the gas to be heated into said chamber} 10. Apparatus asset forth in claim 9 having an are associated with an air cylinder for automatically initiating an are between said first and second electrodes.

References Cited by the Examiner OTHER REFERENCES Acetylene, Encyclopedia of Chemical Technology, Volume 1, pages 107-108, 1947.

initiating means including a carbon electrode operably 15 JOSEPH V. TRUHE, Primary Examiner. 

1. AN ELECTRIC ARC GAS HEATER COMPRISING A FIRST TUBULAR WATER-COOLED ELECTRODE HAVING CLOSURE MEANS AT ONE END THEREOF AND BEING OPEN AT THE OTHER END AND HAVING A LENGTH TO DIAMETER RATIO OF BETWEEN ABOUT 5 TO ABOUT 30; A SECOND TUBULAR WATER-COOLED ELECTRODE OPEN AT BOTH ENDS AND AXIALLY SPACED FROM THE OPEN END OF SAID FIRST ELECTRODE AND HAVING A LENGTH TO DIAMETER RATIO OF BETWEEN ABOUT 5 TO ABOUT 40, THE RATIO OF THE INSIDE DIAMETER OF SAID FIRST TUBULAR ELECTRODE TO THE INSIDE DIAMETER OF SAID SECOND TUBULAR ELECTRODE BEING BETWEEN ABOUT 2.5 TO 0.5; AND THE RATIO OF CURRENT TO INSIDE DIAMETER OF SAID SECOND ELECTRODE BEING BETWEEN ABOUT 50 AND ABOUT 2000 AMP/INCH; A NOZZLE OUTLET CARRIED BY SAID SECOND TUBULAR MEMBER AT ONE END THEREOF; A WATERCOOLED CHAMBER OF SUBSTANTIALLY GREATER DIAMETER THAN AND SURROUNDING THE SPACE BETWEEN SAID TWO ELECTRODES; A PLURALITY OF GAS INJECTION MEANS MOUNTED IN THE WALLS OF SAID CHAMBER AND INCLUDING A TUBULAR MEMBER PROVIDED WITH AN ORIFICE FOR DIRECTING THE GAS TO BE HEATED INTO SAID CHAMBER. 